Tundish stopper rod for continuous molten metal casting

ABSTRACT

Stopper rods for the continuous casting of molten metal have a stopper rod body, and a stopper rod tip at a lower end of the stopper rod body. The stopper rod tip defines a frustroconically shaped exterior surface which terminates in a recessed nose. The recessed nose is most preferably a curvilinear surface (e.g., a spherical segment), but non-curvilinear surfaces (e.g., prismatic, pyramidal, triangular, and quadrangular surfaces) may alternatively be employed. The frustroconically shaped exterior surface of the stopper rod tip most preferably forms an angle θ with respect to a horizontal plane which is sufficiently great so as to increase the velocity of the flowing molten metal to reduce the boundary layer thickness thereof adjacent the nozzle and stopper rod tip surfaces so as to minimize the deposition of inclusions thereon. In addition, the angle θ formed by the frustroconically shaped exterior surface is also most preferably sufficiently small so as to not detrimentally affect the lifting force sensitivities of the stopper rod.

FIELD OF THE INVENTION

The present invention relates generally to the casting of molten metal, such as steel, copper, aluminum and alloys thereof. More specifically, the present invention relates to stopper rods for regulating the flow rate of molten metal discharged from a tundish during a continuous casting operation.

BACKGROUND AND SUMMARY OF THE INVENTION

The continuous casting of molten metal involves providing an available source of molten metal in a suitable vessel, for example, a tundish or ladle, which is located physically above a mold in the continuous casting apparatus. When using a tundish as the vessel for holding the molten metal, a flow of molten metal is discharged therefrom into the mold via a tundish discharge nozzle at a flow rate which is suitable for the casting conditions. The flow rate of molten metal being discharged from the tundish nozzle is controllably regulated by a stopper rod. More specifically, the stopper rod is moveable relative to the tundish nozzle between seated and unseated conditions. Thus, movement of the stopper rod relative to the tundish nozzle will selective adjust the annular orifice area defined between the stopper rod tip and the tundish nozzle through which molten metal is allowed to flow. Adjustably varying the effective annular orifice area will thereby in turn adjustably control over the flow rate of the molten metal being discharged from the tundish.

One problem associated with controlling molten metal flow is that so-called inclusions (e.g., contaminants in the molten metal such as oxidized particles of the metal being cast) are typically present in the molten metal as it is discharged from the tundish through the nozzle. The particular geometry of the stopper rod tip which is capable of seating with the tundish nozzle may create flow profiles which encourage the inclusions to deposit on the surface of the stopper rod and/or tundish nozzle. Over time, therefore, the geometry of the orifice are defined between the tundish nozzle and the stopper rod tip may change due to continual deposit of inclusions thereby eventually detrimentally affecting the stopper rod's flow control characteristics.

It would therefore be desirable if a stopper rod for continuous molten metal casting could be provided which minimizes (if not eliminates entirely) deposition of inclusions onto the stopper rod tip thereby allowing the stopper rod to be maintained in service for prolonged time periods and/or improving steel cleanliness. It is towards fulfilling such a need that the present invention is directed.

Broadly, the present invention is embodied in a stopper rod for continuous molten metal casting which creates flow profiles of the molten metal as it is being discharged from a vessel holding the molten metal through a nozzle so as to enhance metal cleanliness. That is, the stopper rods according to the present invention discourage the deposition of inclusions (e.g., undesirable particulates, such a metal oxides) onto the stopper rod tip. According to one especially preferred aspect of the present invention, a stopper rod for continuous molten metal casting is provided which has a geometric profile so as to increase the velocity of the flowing molten metal sufficient to reduce the boundary layer thickness of such flowing molten metal adjacent the nozzle and stopper rod tip surfaces so as to minimize the deposition of inclusions thereon.

Advantageously, the geometric profile of the stopper rod tip according to the present invention also does not detrimentally affect the lifting force sensitivities of the stopper rod. That is, the geometric profile of the stopper rod tip does not create molten metal flow profiles which would make it difficult to exercise physical displacement of the stopper rod tip relative to the tundish nozzle. As a result, the stopper rods of the present invention exhibit a relatively wide range of flow rate control of the molten metal flow discharged from the tundish.

According to a particularly preferred aspect of the invention, a tundish stopper rod for continuous casting of molten metal is provided and comprises a stopper rod body, and a stopper rod tip at a lower end of the stopper rod body, wherein the stopper rod tip has a frustroconically shaped exterior surface which terminates in a recessed nose. Advantageously the recessed nose is a recessed curvilinear surface (e.g., a spherical segment, but non-curvilinear surfaces (e.g., prismatic, pyramidal, triangular, and quadrangular surfaces) may also be provided.

In especially preferred embodiments, the frustroconically shaped surface forms an angle θ with a horizontal surface which is between about 55° to about 75°, and more preferably, about 65°± about 7°. A central vent channel and tip vent channel are advantageously formed in the stopper rod body and stopper rod tip, respectively, to allow venting of off-gases.

A system for continuous casting of molten metal in accordance with the present invention will most preferably comprise a vessel for holding a supply of molten metal to be cast, a discharge nozzle for discharging molten metal from the vessel, and a stopper rod mounted for reciprocal rectilinear movements towards and away from the discharge nozzle to allow flow rate regulation of the molten metal discharged from the vessel through the discharge nozzle, wherein the stopper rod includes a stopper rod body, and a stopper rod tip at a lower end of the stopper rod body, the stopper rod tip having a frustroconically shaped exterior surface which terminates in a recessed nose. Advantageously, the vessel is a tundish or a ladle.

According to the present invention, the flow rate of molten metal being discharged from a vessel through a discharge nozzle during a continuous casting operation may be regulated by providing a stopper rod comprising a stopper rod body, and a stopper rod tip at a lower end of the stopper rod body, the stopper rod tip having a frustroconically shaped exterior surface which terminates in a recessed nose. The stopper rod may be positioned within the vessel so that the stopper rod tip operatively cooperates with the discharge nozzle. Therefore, by controllably displacing the stopper rod tip relative to the discharge nozzle, the flow rate of molten metal being discharged from the vessel through the tundish discharge nozzle may be regulated.

These and other aspects and advantages will become more apparent after careful consideration is given to the following detailed description of the preferred exemplary embodiments thereof.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

Reference will hereinafter be made to the accompanying drawings, wherein like reference numerals throughout the various FIGURES denote like structural elements, and wherein;

FIG. 1 is a schematic cross-sectional elevational view of a tundish having a stopper rod for continuous molten metal casting according to an especially preferred embodiment of the present invention;

FIG. 2 is a cross-sectional elevational view of the stopper rod depicted in FIG. 1;

FIG. 3 is an enlarged detailed cross-sectional view of the stopper rod tip; and

FIG. 4 is a bar graph of the percent of trapped inclusions in the molten metal that can expected to be trapped on the refractory surfaces of a stopper rod in accordance with the present invention in comparison to stopper rods outside the scope of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Accompanying FIG. 1 depicts a continuous casting tundish system 10 which includes a tundish 12 for containing a supply of molten metal 14 therein. The molten metal 14 is introduced into the tundish 10 by a tundish inlet nozzle 16, and is discharged from the tundish through the tundish discharge nozzle 18. Typically, the tundish discharge nozzle is connected to an immersion nozzle 20 associated with the continuous casting mold (not shown) so as to transfer the molten metal to the mold. Although a tundish 12 is shown and will be referenced specifically hereinafter, a ladle may also be employed as the vessel for holding the molten metal 14. However, for ease of discussion, a tundish 12 will be described specifically below as it represents an especially preferred vessel for use in the present invention.

A stopper rod 22 in accordance with the present invention is mounted for reciprocal rectilinear movements relative to the tundish discharge nozzle 18 so that the stopper rod tip 22-1 is capable of substantial vertically displacements towards and away from the nozzle 18 (arrow A1 in FIG. 1). Displacement of the stopper rod tip 22-1 thereby varies the orifice area defined with the nozzle 18 which in turn controls the flow rate of the molten metal being discharged therethrough. In this regard, the stopper rod 22 includes a cross-pin 22-2 which is coupled to an arm 24 associated with a lifting mechanism, for example, a hydraulic actuator (not shown).

The stopper rod 22 according to the present invention is perhaps more clearly depicted in accompanying FIGS. 2 and 3. As shown therein, the stopper rod 22 is an elongate generally cylindrical stopper rod body member 22-3 which is tapered somewhat between its upper end 22-4 and its lower end 22-5. The stopper rod body 22-3 is most preferably formed of a high temperature ceramic material adapted to being immersed in molten metal.

The stopper rod tip 22-1 is joined to the lower end of the stopper rod body 22-3 at the lower end 22-5 thereof and is also most preferably formed of a high temperature ceramic material adapted to being immersed into molten metal. The stopper rod tip 22-1 may be formed of the same or different ceramic material as compared to the stopper rod body 22-3. In addition, although the stopper rod body 22-3 and tip 22-1 are depicted as separate structural component, they could for example be formed as a unitary structure is desired.

A tip vent channel 22-6 is centrally formed in the stopper rod tip 22-1 and communicates with the central vent channel 22-7 formed in the stopper rod body 22-3. The tip vent channel 22-6 is most preferably a smaller diameter as compared to the central vent channel 22-7. Collectively, the vent channels 22-6 and 22-7 allow off-gas that may be generated by the ceramic materials forming the stopper rod body 22-3 and/or tip 22-1 to be vented out of the tundish 12 so it does not contaminate the molten metal 14 therein. Although vent channels 22-6 and 22-7 are shown in the accompanying FIGS. 1-3, the stopper rod 22 in accordance with the present invention could be provided without any such vent channels. In addition, a channel through the tip 22-1 may be provided and is especially useful if an inert purge gas is desired to be introduced therethrough.

An aperture 22-8 is formed through the stopper rod body 22-3 so as to receive the cross-pin 22-2. Alternative means of lifting the stopper rod 22 may also be provided. For example, a threaded nut may be physically embedded or affixed to the upper end of the stopper rod body 22-3 so that the stopper rod 22 may be threadably attached to a lifting rod. Alternatively or additionally, an external pressure collar may be attached to the upper end of the stopper rod body 22-3 for such purpose.

Important to the present invention, the stopper rod tip 22-1 has a frustroconically shaped exterior surface 22-1 a which includes a recessed nose 22-1 b. Most preferably, the recessed nose 22-1 b is a smoothly arcuate concavity such as a spherical segment. However, virtually any concavity may be employed in the practice of the present invention. Thus, the recessed nose 22-1 b may be embodied in regular and irregular curvilinear surfaces. Alternatively, non-curvilinear surfaces (e.g., prismatic, pyramidal, triangular, quadrangular and the like) may be employed to form the recessed nose 22-1 b.

The frustroconically shaped exterior surface 22-1 a of the stopper rod tip 22-1 most preferably forms an angle θ with respect to a horizontal plane which is sufficiently great so as to increase the velocity of the flowing molten metal to reduce the boundary layer thickness thereof adjacent the nozzle and stopper rod tip surfaces so as to minimize the deposition of inclusions thereon. In addition, the angle θ formed by the frustroconically shaped exterior surface 22-1 a is also sufficiently small so as to not detrimentally affect the lifting force sensitivities of the stopper rod 22. Advantageously, the frustroconically shaped exterior surface 22-1 a of the stopper rod tip 22-1 forms an angle θ with a horizontal surface which is between about 55° to about 75°. According to a particularly preferred embodiment of the invention, the angle θ formed by the frustroconically shaped exterior surface 22-1 a is about 65°± about 7°.

The present invention will be further understood by reference to the following non-limiting Examples.

EXAMPLES

Computer simulations were conducted based on a mathematical fluid turbulence model coupled with a Lagrange model for trajectory of particles. The selected model for momentum transfer was the turbulent regime known as k-ε. A constant casting rate of 4.0 tons/minute was simulated for each of the stopper rods being examined.

Comparative Stopper Rod No. 1 (CSR1) was formed with a stopper rod tip configured to have an upper cylindrical surface portion, an intermediate frustroconical surface portion, and a terminal smoothly convex nose. The Comparative Stopper Rod No. 2 (CSR2) was formed with a stopper rod tip having a hemi-ellipsoidal surface configuration. The stopper rod according to the present invention was configured as shown in FIGS. 1-3 above. A bar graph plot of percentage of trapped inclusions to form a clog for each of the stopper rods is shown in FIG. 4. It is evident that the stopper rod according to the present invention results in substantially less percentage of trapped inclusions as compared to the stopper rods CSR1 and CSR 2 outside the scope of this invention.

While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims. 

1. A stopper rod for continuous casting of molten metal comprising a stopper rod body, and a stopper rod tip at a lower end of the stopper rod body, said stopper rod tip having a frustroconically shaped exterior surface which terminates in a recessed nose.
 2. The stopper rod of claim 1, wherein the recessed nose is a recessed curvilinear surface.
 3. The stopper rod of claim 2, wherein the recessed curvilinear surface is a spherical segment.
 4. The stopper rod of claim 1, wherein the recessed nose is a recessed non-curvilinear surface.
 5. The stopper rod as in claim 4, wherein the recessed non-curvilinear surface is selected from prismatic, pyramidal, triangular, and quadrangular surfaces.
 6. The stopper rod as in claim 1, wherein the frustroconically shaped surface forms an angle θ with a horizontal surface which is between about 55° to about 75°.
 7. The stopper rod as in claim 6, wherein the angle θ is about 65°± about 7°.
 8. The stopper rod as in claim 1, comprising a vent channel formed in the stopper rod body.
 9. The stopper rod as in claim 8, wherein the stopper rod tip includes a tip vent channel joined to the stopper rod body vent channel.
 10. A system for continuous casting of molten metal comprising: a vessel for holding a supply of molten metal to be cast; a discharge nozzle for discharging molten metal from the vessel; and a stopper rod mounted for reciprocal rectilinear movements towards and away from the discharge nozzle to allow flow rate regulation of the molten metal discharged from the vessel through the discharge nozzle, wherein said stopper rod includes, (i) a stopper rod body, and (ii) a stopper rod tip at a lower end of the stopper rod body, (iii) said stopper rod tip having a frustroconically shaped exterior surface which terminates in a recessed nose.
 11. The system of claim 10, wherein the recessed nose of the stopper rod tip is a recessed curvilinear surface.
 12. The system of claim 11, wherein the recessed curvilinear surface is a spherical segment.
 13. The system of claim 10, wherein the recessed nose of the stopper rod tip is a recessed non-curvilinear surface.
 14. The system as in claim 13, wherein the recessed non-curvilinear surface is selected from prismatic, pyramidal, triangular, and quadrangular surfaces.
 15. The system as in claim 10, wherein the frustroconically shaped surface forms an angle θ with a horizontal surface which is between about 55° to about 75°.
 16. The system as in claim 10, wherein the angle θ is about 65°± about 7°.
 17. The system as in claim 10, wherein the stopper rod further includes a vent channel formed in the stopper rod body.
 18. The system as in claim 17, wherein the stopper rod tip includes a tip vent channel joined to the stopper rod body vent channel.
 19. The system as in claim 10, wherein the stopper rod further includes a cross-pin adapted to being attached to a lifting mechanism.
 20. The system as in claim 10, wherein the vessel is a tundish.
 21. A method of regulating flow rate of molten metal being discharged from a vessel through a discharge nozzle during a continuous casting operation, the method comprising: (a) providing a stopper rod comprising a stopper rod body, and a stopper rod tip at a lower end of the stopper rod body, said stopper rod tip having a frustroconically shaped exterior surface which terminates in a recessed nose; and (b) positioning the stopper rod within the vessel so that the stopper rod tip operatively cooperates with the discharge nozzle; and (c) controllably displacing the stopper rod tip relative to the discharge nozzle so as to regulate the flow rate of molten metal being discharged from the tundish through the tundish discharge nozzle.
 22. The method of claim 21, wherein step (b) comprises positioning the stopper rod within a tundish. 